The proposed research will develop and evaluate software extensions to CT Colonography in order to implement a more easily tolerated, non-invasive method of colon cancer screening. Preliminary data indicate that CT Colonography (CTC, or "Virtual Colonoscopy") is a sensitive method for detecting clinically significant colonic polyps. However, the technique currently suffers two limitations: 1) patients are still required to undergo cleansing purgation of the bowel prior to imaging -- a step that is an important compliance barrier -- and 2), the lengthy evaluation time for each exam limits implementation of CTC for time-efficient screening. Image processing techniques have the potential to address these hindrances of CTC. Digital subtraction bowel cleansing (DSBC) is a method for CTC in which post processing software effects a computerized cleaning of marked colonic contents from CT images, thereby greatly reducing the duress of pre-exam bowel preparation. Automated polyp detection is a technique wherein mathematical algorithms identify for the evaluating radiologist potential lesions on CT images, reducing evaluation time. The candidate, Dr. Zalis, has an excellent background in computer science and clinical radiology. In the short run, Dr. Zalis will execute the proposed research in the process, consolidating his skills as a technically oriented clinical researcher. Within the next three years, Dr. Zalis intends to initiate a larger trial of CTC in a screening population, using the data and experience obtained in the current proposal. Dr. Zalis' long-term interest is to develop and clinically evaluate computer-based tools to aid in the interpretation of radiologic studies. The host department of radiology at Massachusetts General Hospital has an established program in CTC. Our preliminary data suggest DSBC results in improved patient comfort for CT Colonography and that polyp detection software can identify significant lesions. Both techniques are in preliminary stages of development, and require further refinement. In the short term, we will refine and assess the diagnostic performance DSBC and automated polyp detection in CTC. The proposed research will serve as basis for the design of a larger, screening-cohort evaluation of CTC using these image-processing techniques.